Optical pulse buffers are important for optical communications and ultra-fast computing. An exemplary preferred type of buffer, comprising an optical fiber coil, is disclosed in my co-pending U.S. patent application Ser. No. 12/587,767, filed Oct. 13, 2008. In this preferred buffer, the radii of the optical fiber and coil are selected to confine the propagating fundamental mode in a region that is shifted away from the center of the optical fiber, thus significantly reducing both propagation loss and bend loss along the device.
While the confinement of the propagating mode to a shifted, peripheral region of the optical fiber improves the performance of the device, difficulties remain in coupling an input signal to the optical fiber coil, or extracting an optical signal therefrom. One problem may be associated with the large mismatch between the coil and a conventional input/output waveguide or fiber in terms of, for example, physical dimension, modefield diameter and propagation constant.
There remains a need for providing low loss coupling from a conventional fiber (or, perhaps, a planar waveguide) into or out of the shifted fundamental mode of an optical signal propagating along an optical fiber coil.